fix(core): tend to history with dangling function calls/responses (#7692)

packages/core/src/services/loopDetectionService.ts

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+import type { Content } from '@google/genai';
 import { createHash } from 'node:crypto';
 import type { ServerGeminiStreamEvent } from '../core/turn.js';
 import { GeminiEventType } from '../core/turn.js';
@@ -11,6 +12,10 @@ import { logLoopDetected } from '../telemetry/loggers.js';
 import { LoopDetectedEvent, LoopType } from '../telemetry/types.js';
 import type { Config } from '../config/config.js';
 import { DEFAULT_GEMINI_FLASH_MODEL } from '../config/config.js';
+import {
+  isFunctionCall,
+  isFunctionResponse,
+} from '../utils/messageInspectors.js';
 
 const TOOL_CALL_LOOP_THRESHOLD = 5;
 const CONTENT_LOOP_THRESHOLD = 10;
@@ -328,12 +333,35 @@ export class LoopDetectionService {
     return originalChunk === currentChunk;
   }
 
+  private trimRecentHistory(recentHistory: Content[]): Content[] {
+    // A function response must be preceded by a function call.
+    // Continuously removes dangling function calls from the end of the history
+    // until the last turn is not a function call.
+    while (
+      recentHistory.length > 0 &&
+      isFunctionCall(recentHistory[recentHistory.length - 1])
+    ) {
+      recentHistory.pop();
+    }
+
+    // A function response should follow a function call.
+    // Continuously removes leading function responses from the beginning of history
+    // until the first turn is not a function response.
+    while (recentHistory.length > 0 && isFunctionResponse(recentHistory[0])) {
+      recentHistory.shift();
+    }
+
+    return recentHistory;
+  }
+
   private async checkForLoopWithLLM(signal: AbortSignal) {
     const recentHistory = this.config
       .getGeminiClient()
       .getHistory()
       .slice(-LLM_LOOP_CHECK_HISTORY_COUNT);
 
+    const trimmedHistory = this.trimRecentHistory(recentHistory);
+
     const prompt = `You are a sophisticated AI diagnostic agent specializing in identifying when a conversational AI is stuck in an unproductive state. Your task is to analyze the provided conversation history and determine if the assistant has ceased to make meaningful progress.
 
 An unproductive state is characterized by one or more of the following patterns over the last 5 or more assistant turns:
@@ -347,7 +375,7 @@ For example, a series of 'tool_A' or 'tool_B' tool calls that make small, distin
 
 Please analyze the conversation history to determine the possibility that the conversation is stuck in a repetitive, non-productive state.`;
     const contents = [
-      ...recentHistory,
+      ...trimmedHistory,
       { role: 'user', parts: [{ text: prompt }] },
     ];
     const schema: Record<string, unknown> = {